Grow a Brain, Already

How do you know that you aren’t just a brain in a vat of bubbling chemicals, hooked up to a virtual-reality simulator? Are your hands and feet real? And what about your spouse, your child, and your dog? Are they just figments of an imagination fed by a computer that simulates what it would be like if you were an ordinary human being with an ordinary body? Until last week, I would have said that your best hope for being more than a bodiless brain in a chemical stew was the fact that no scientist was yet capable of sustaining a viable brain in a jar. The whole concept was a thought experiment—merely the kind of the thing that amused philosophers and science-fiction writers.

But a paper just published in the journal Nature has shown that it is possible to sustain a rudimentary brain in a vat. It has also demonstrated that it is possible to synthesize one, from scratch—or from a lattice of stem cells, at least. For now the results are pretty crude; nobody will be growing replacement parts for your frontal cortex next week. The “cerebral organoids” that researchers were able to produce are akin to the neural precursors that you would find in an embryo, nine weeks or so after conception. They are not yet wired up; they’ve not had any experience; they have no thoughts, no ideas, no emotions. They are, at best, brains-in-training, and nothing that anyone would mistake for real brains.

Yet the implications of this new study are profound: if the leading-edge scientists of 2013 can grow a brain rudiment in a dish, who is to say what the scientists of 2063 will be able to do? In May, a team from Princeton “merge[d] biologic and nanoelectronic functionalities” to 3-D-print a bionic ear, while earlier this month people chomped on the first lab-grown hamburger, which Michael Specter had written about in the magazine.

As the technology for fabricating brains develops, perhaps first by building specific parts—say, a new amygdala, which processes emotion, among other functions—and ultimately toward the synthesis of complete brains, a whole new set of medical possibilities might emerge. An accident victim could receive an entire brain transplant. Or, if the language areas of a brain are destroyed by a stroke, a replacement part could simply be ordered.

The technical obstacles remain formidable: we don’t know enough about how the brain’s language areas work, or how to integrate foreign tissue into them, or how to “program” them so that, for example, a neurolinguistic transplant came equipped with knowledge of English rather than factory fresh (like a newborn), without a language installed.

There’s no principled reason to think that any of these technical obstacles are insurmountable, though. And once the race to build replacement brain parts is on, it’s certain that eager neuroscientists and industrialists will try to build entire brains, too.

But we’ll also need to confront immense ethical quandaries. What rights does synthetic brain tissue have? Should a 3-D-printed brain have the right to vote? To an education? To terminate its own life? (Or to not be terminated?) For now, these questions are still just another round of thought experiments. But it’s more likely than ever that such thoughts might some day be held by just another brain in a jar.

Photograph: Science & Society Picture Library/SSPL/Getty.

Gary Marcus is a professor of cognitive science at N.Y.U. and the author of “Guitar Zero.”